Chapter 4, “Troubleshooting IPv4 Routing Part I,” began the discussion of IPv4 troubleshooting, looking at the usual first steps when troubleshooting a problem. This chapter moves on to a later stage, when the problem has been isolated to a smaller part of the network, and to a smaller set of possible causes of the problem. The topics in this chapter get specific and look for those root causes: the causes of network problems that have specific solutions that, once a change is made, will solve the original problem.

This chapter breaks down the discussion based on the two major divisions in how packets are forwarded in an IPv4 internetwork. The first half of the chapter focuses on the root causes of problems between a host and its default router. The second half looks at the routers that forward the packet over the rest of a packet’s journey, from the router acting as default router all the way to the destination host.

Note that in addition to Chapters 4 and 5, other chapters in this book discuss troubleshooting topics that help when troubleshooting IPv4 internetworks. In particular, Chapter 11, “Troubleshooting IPv4 Routing Protocols,” discusses troubleshooting IPv4 routing protocols, namely Open Shortest Path First (OSPF) and Enhanced Interior Gateway Routing Protocol (EIGRP). Chapter 3, “Troubleshooting LAN Switching,” discussed how to troubleshoot LAN issues. Some topics inside the chapters in Part IV explain how to troubleshoot WAN links. Finally, Chapter 16, “Troubleshooting IPv6 Routing,” discusses how to apply these same IPv4 troubleshooting concepts to IPv6.

“Do I Know This Already?” Quiz

The troubleshooting chapters of this book pull in concepts from many other chapters, including some chapters in Cisco CCENT/CCNA ICND1 100-101 Official Cert Guide. They also show you how to approach some of the more challenging questions on the CCNA exams. Therefore, it is useful to read these chapters regardless of your current knowledge level. For these reasons, the troubleshooting chapters do not include a “Do I Know This Already?” quiz. However, if you feel particularly confident about troubleshooting IP routing features covered in this book and Cisco CCENT/CCNA ICND1 100-101 Official Cert Guide, feel free to move to the “Exam Preparation Tasks” section near the end of this chapter to bypass the majority of the chapter.